Copper alloy for electrical and electronic parts and semiconductors with high strength and high electrical conductivity and method of preparing the same

ABSTRACT

Disclosed are a copper alloy for electrical and electronic parts and semiconductors having high strength and high electrical conductivity and a method of preparing the same. The copper alloy includes 0.09 to 0.20% by mass of iron (Fe), 0.05 to 0.09% by mass of phosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of copper (Cu) and 0.05% by mass or less of inevitable impurities, and has tensile strength of 470 MPa or more, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or higher.

TECHNICAL FIELD

The present invention relates to a copper alloy for electrical and electronic parts and semiconductors with high strength and high electrical conductivity and a method of preparing the same, and more particularly, to a copper alloy including copper (Cu), iron (Fe), phosphorous (P) and manganese (Mn) and a method of preparing the same.

BACKGROUND

As copper alloy used for various purposes, i.e., used as materials for semiconductor lead frames, electrical and electronic parts, etc., a Cu—F—P-based alloy including Fe and P is generally used. For example, among copper alloys, a copper alloy C19210 including 0.05-0.15% by mass of Fe and 0.025-0.04% by mass of P or a copper alloy C19400 including 2.1-2.6% by mass of Fe, 0.015-0.15% by mass of P and 0.05-0.2% by mass of Zn have excellent strength and electrical conductivity and thus are widely used as a material for lead frames. The reason why Fe and P are mainly used as additive elements is that they form a precipitation phase in a copper matrix so as to impart excellent strength and electrical conductivity.

However, out of various characteristics of copper alloys, strength and electrical conductivity conflict with each other, i.e., are inversely proportional to each other, and thus, as strength is increased, electrical conductivity is inevitably decreased and, as electrical conductivity is increased, strength is inevitably decreased. Therefore, the conventional copper alloy C19210 having tensile strength of 400 MPa and electrical conductivity of 80% IACS has poor strength but has excellent electrical conductivity and is thus used in products requiring high electrical conductivity, and the conventional copper alloy C19400 having tensile strength of 500 MPa and electrical conductivity of 60% IACS has poor electrical conductivity but has excellent strength and is thus used in products requiring high strength.

Recently, according to thin-profile and miniaturization trends of electrical and electronic parts, characteristics of materials become more important. As semiconductor devices used in electronic equipment, vehicles, etc., are developed towards large-capacity, miniaturization and high-integration trends, miniaturization and thin-profile of lead frames used in the semiconductor devices are carried out now. Therefore, copper alloys simultaneously provide high strength, high electrical conductivity and excellent workability, as compared to the conventional copper alloys, and simultaneously satisfying tensile strength of 470 MPa or more and electrical conductivity of 75% IACS or more according to decrease in the thicknesses of electronic products are required. Therefore, in order to satisfy such requirements in the industrial fields, efforts are being made to improve both strength and electrical conductivity, which conflict with each other.

In order to increase strength of a copper alloy, Fe and P contents are increased or a third element, such as Sn, Mg or Ni, is added, but when the contents of these elements are increased, strength of the copper alloy is increased but electrical conductivity of the copper alloy is lowered. Therefore, instead of addition of elements, crystal grains are refined or size and distribution of crystallized and precipitated substances are controlled so as to improve characteristics of a copper alloy. However, in this case, various problems, such as surface defects, lowering of reliability, non-uniform microstructures, etc., occur. Therefore, improvement in both strength and electrical conductivity of copper alloys is a difficult and important research subject.

Further, a process of applying heat is executed in fields to which copper alloys are applied, and thus, copper alloys require a property of withstanding heat and such a property is referred to as softening resistance which may be evaluated as a softening resistant temperature. The softening resistant temperature means a heat treatment temperature which, when a hardness value of a prepared copper alloy sheet changed after heat treatment for 1 minute is measured, corresponds to 80% of an initial hardness value (prior to heat treatment). The softening resistant temperature is used as an index indicating whether or not the corresponding material withstand heat and is connected to reliability of a finished product, as described above. In conventional semiconductor packages or electronic parts, a copper alloy having a softening resistant temperature of about 380° C. causes no problems in manufacture of products and reliability of final products. However, copper alloys which are recently applied to semiconductor packages, electronic parts, etc. require better softening resistance due to addition of a process of applying heat, such as soldering or wire-bonding, in processing of products, and thus, improvement in softening resistance to a softening resistant temperature of 400° C. or higher is required.

Various patents relating to acquisition of strength and electrical conductivity required by copper alloy materials for lead frames have been filed.

Korean Patent Laid-open Publication No. 10-2008-0019274 discloses improvement in strength of a Cu—Fe—P-based alloy by adding Mg. However, when Mg is added to the alloy, electrical conductivity of the alloy is inevitably lowered. When Mg is added to the conventional Cu—Fe—P-based alloy, the alloy exhibits tensile strength of 450 MPa and electrical conductivity of 70% IACS which are below characteristics recently required by lead frames (tensile strength of 470 MPa or more and electrical conductivity of 77% IACS or more), and the reason for this is due to a coarse Mg—P-based crystallized substance. When Mg is added to the alloy, strength and electrical conductivity of the alloy are inevitably lowered due to the coarse Mg—P-based crystallized substance, inevitably generated from starting of casting to ending of hot rolling, and defects.

Further, Korean Patent Application Publication No. 10-2005-0076767 discloses improvement in strength of a Cu—Fe—P-based alloy by controlling the particle size of precipitates in the alloy. However, in this Patent Document, in order to finely control the particle size of the precipitates, cold rolling and annealing processes are executed two or more times, and thus, various variables exist and it is difficult to actually prepare such an alloy on an industrial scale. Further, this Patent Document describes that a volume fraction of the precipitates is 1% or more and the number of particles of the precipitates of 300/μm² or more, but the volume fraction is a value including the number of coarse particles.

In addition, Korean Patent Application Publication No. 10-2013-0136183 discloses improvement in strength of a Cu—Fe—P-based alloy by adding Mn to the alloy, but the prepared alloy does not satisfy strength and electrical conductivity required actually at industrial sites. Further, claim 4 of this Patent Document describes that the particle sizes of precipitates are 10-30 μm, but, substantially, the particle sizes of 10-30 μm are excessively large and these particles correspond to casting defects or foreign substances rather than the precipitates and thus do not improve strength and electrical conductivity. In this regard, if particles having a size of 10-30 μm exist within a copper alloy, characteristics of the copper alloy are deteriorated and it is difficult to execute a semiconductor packaging process due to poor surface quality. Further, the above Patent Document does not describe any analysis results or grounds to determine a kind of the precipitates, and only grain boundaries rather than precipitates are observed in SEM analysis results shown in FIG. 3 and may not provide technical grounds.

SUMMARY Object to be Solved

An object of the present invention is to provide a copper alloy for electrical and electronic parts and semiconductors which has strength and electrical conductivity, which satisfies characteristics recently required in the industrial world, not satisfied by conventional technologies, and have excellent softening resistance, and a method of preparing the same.

Means for Solving Object

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a copper alloy for electrical and electronic parts and semiconductors includes 0.09 to 0.20% by mass of iron (Fe), 0.05 to 0.09% by mass of phosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of copper (Cu) and 0.05% by mass or less of inevitable impurities, wherein the inevitable impurities includes at least one selected from the group consisting of Si, Zn, Ca, Al, Ti, Be, Cr, Co, Ag and Zr, and the copper alloy has tensile strength of 470 MPa or more, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or higher. The impurities may have a content of 0.01% by mass or less. The copper alloy for electrical and electronic parts and semiconductors may further include 0.0001 to 0.03% by mass of at least one of Ni or Sn.

The copper alloy may have an average crystal grain size of 20 μm or less and a standard deviation of 5 μm or less, out of crystal grain sizes measured by crystal orientation analysis using a field emission scanning electron microscope (FE-SEM).

The copper alloy includes (FeMn)₂P precipitates. The (FeMn)₂P precipitates may be measured by observing a specimen prepared by a carbon extraction replica method using a high-resolution transmission electron microscope (HR-TEM) or a field emission transmission electron microscope (FE-TEM) at a magnification of 100,000× or more, and have an average particle size of 50 nm or less and an area density of 1.01*10¹⁰/cm² or more.

The copper alloy may be prepared as a sheet or a panel.

In another aspect of the invention, a method of preparing a copper alloy for electrical and electronic parts and semiconductors includes melting the above-described component elements to cast an ingot, homogenization heat treating the acquired ingot at a temperature of 900-1,000° C. for 1-4 hours and then hot rolling at a working ratio of 85-95%, cold rolling the obtained product from the previous step at a working ratio of 87-98%, precipitation heat treating the obtained product from the previous step at a temperature of 430-520° C. for 1-10 hours, and rolling the obtained product from the previous step at a reduction ratio of 10-90% to produce a finished product.

Effects of the Invention

A copper alloy in accordance with the present invention has excellent strength and electrical conductivity and has outstanding softening resistant characteristics. Further, when a copper alloy is prepared through a preparation process in accordance with the present invention, in spite of decrease in process costs, the acquired copper alloy exhibits excellent strength and electrical conductivity and is applicable to various electrical and electronic parts in addition to discrete transistors and semiconductor lead frames.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graph illustrating softening resistant characteristics of a copper alloy prepared according to Example 5 and a conventional copper alloy.

FIG. 2A is an FE-SEM photograph representing microstructures after hot rolling at a temperature of 870° C. in a process of preparing a copper alloy having a composition stated in Example 1.

FIG. 2B is an FE-SEM photograph representing microstructures after hot rolling at a temperature of 900° C. in the process of preparing the copper alloy having the composition stated in Example 1.

FIG. 2C is an FE-SEM photograph representing microstructures after hot rolling at a temperature of 950° C. in the process of preparing the copper alloy having the composition stated in Example 1.

FIG. 3 is an FE-SEM photograph representing microstructures of a copper alloy prepared according to Example 5.

FIG. 4A is an FE-TEM photograph of a specimen prepared by an ion milling method, in order to confirm precipitates in the copper alloy having a composition of Example 5.

FIG. 4B is an FE-TEM photography of a specimen prepared by a carbon extraction replica method, in order to confirm the precipitates in the copper alloy having the composition of Example 5.

DETAILED DESCRIPTION

The present invention provides a copper alloy for electrical and electronic parts and semiconductors with high strength and electrical conductivity and excellent softening resistance and a method of preparing the same. In the following description, % representing the content of a component element is % by mass, unless stated otherwise.

Copper Alloy in Accordance with the Invention

A copper alloy in accordance with the present invention includes 0.09 to 0.20% by mass of iron (Fe), 0.05 to 0.09% by mass of phosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of copper (Cu) and 0.05% by mass or less of inevitable impurities, the inevitable impurities include at least one selected from the group consisting of Si, Zn, Ca, Al, Ti, Be, Cr, Co, Ag and Zr, and the copper alloy is a copper alloy for electrical and electronic parts or semiconductors which has tensile strength of 470 MPa or more, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or more.

Hereinafter, a component composition of the copper alloy in accordance with the present invention will be described. In the following description, % representing the content of an element is % by mass, unless stated otherwise.

[Fe]

Fe is an element necessary to form fine (FeMn)₂P precipitates so as to improve strength or conductivity. An Fe content is within the range of 0.09 to 0.20%. If the Fe content is less than 0.09%, particles necessary to form the precipitates are insufficient and suppression effects of growth of crystal grains due to the precipitates are lowered. As a result, an average crystal grain size or a standard deviation of the average crystal grain is excessively increased, and thus, strength is lowered. Therefore, in order to efficiently exhibit the effects, the Fe content needs to be 0.09% or more. However, if the Fe content exceeds 0.20%, i.e., is excessively increased, coarsening of precipitates is caused, the standard deviation of the average crystal grain is excessively increased, and thus, bending workability and electrical conductivity are lowered.

[P]

In addition to deacidification, P combines with Fe and Mn and thus forms fine (FeMn)₂P precipitates so as to improve strength or conductivity of the copper alloy. A P content is 0.05 to 0.09%. If the P content is less than 0.05%, formation of the fine precipitates is not sufficient and suppression effects of growth of crystal grains due to the precipitates are lowered. As a result, an average crystal grain size or a standard deviation of the average crystal grain is excessively increased, and thus, strength is lowered. Therefore, the P content needs to be 0.05% or more. However, if the P content exceeds 0.09%, i.e., is excessively increased, coarse precipitate particles are increased, the standard deviation of the average crystal grain is excessively increased, and thus, bending workability is lowered. Further, electrical conductivity is lowered.

[Mn]

It is reported that Mn added to a copper alloy generally contributes to improvement in strength of the copper alloy but, if Mn is simply added to the copper alloy to improve strength, electrical conductivity of a finally acquired product of the copper alloy is inevitably lowered. In the copper alloy in accordance with the present invention, the (FeMn)₂P precipitates are formed, and thus, both strength and electrical conductivity of the copper alloy may be simultaneously improved. In the copper alloy in accordance with the present invention, a Mn content is 0.05 to 0.20%. If the Mn content is less than 0.05%, formation of the precipitates is not sufficient and suppression effects of growth of crystal grains due to the precipitates are lowered, and thus, strength is lowered, as in Fe. However, if the Mn content exceeds 0.20%, both strength and electrical conductivity are lowered due to coarse crystallized substances or casting defects.

[Inevitable Impurities]

Further, the copper alloy in accordance with the present invention includes 0.05% or less of at least one selected from the group consisting of Si, Zn, Ca, Al, Ti, Be, Cr, Co, Ag and Zr. Preferably, the impurities content is 0.01% or less. These elements are elements serving to improve various characteristics of the copper alloy and may be selectively added according to application.

In the copper alloy in accordance with the present invention, if Mg which is widely known as having excellent reinforcement effects is added to the copper alloy, strength of a finally acquired product of the copper alloy is somewhat improved but electrical conductivity of the product is inevitably lowered, and Mg reacts with P and causes a coarse Mg—P-based crystallized substance and defects from starting of casting to ending of hot rolling. Therefore, Mg should be excluded.

[Ni] and [Sn]

The copper alloy in accordance with the present invention may further include 0.0001% to 0.03% of at least one of Ni or Sn. Ni is dissolved in a Cu matrix, thus has an effect of improving strength and is effective to provide heat resistance. If the Ni content is less than 0.0001%, strength of the copper alloy cannot be improved and, if the Ni content exceeds 0.03%, electrical conductivity of the copper alloy is lowered.

Sn is a solid-solution strengthening alloy element which is dissolved in a Cu matrix so as to improve strength. If the Sn content is less than 0.0001%, it is difficult to expect improvement in strength of the copper alloy and, if the Sn content exceeds 0.03%, electrical conductivity of the copper alloy is lowered.

[Characteristics of Copper Alloy in Accordance with the Invention]

In general, in copper alloys, as strength of a copper alloy is increased, electrical conductivity of the copper alloy is decreased, and thus, it is difficult to control two characteristics.

The strength of the copper alloy in accordance with the present invention may satisfy both tensile strength of 470 MPa or more and hardness of 145 Hv or more. These are values in which recently required characteristics in the industrial world are reflected and, if strength and electrical conductivity of the copper alloy having an inverse relationship are considered, may be regarded as limits.

Further, copper alloys used in semiconductors or electrical and electronic parts should have electrical conductivity of 75% IACS or more. If electrical conductivity of a copper alloy is less than 75% IACS, transmission of electrical signals is not effective and thus the copper alloy may not be used in products. Electrical conductivity of the copper alloy in accordance with the present invention is 75% IACS or more.

That is, the copper alloy in accordance with the present invention has excellent characteristics, i.e., both improved strength and electrical conductivity.

The copper alloy in accordance with the present invention has an excellent softening resistant temperature of 400° C. or higher. A detailed description of the softening resistant temperature will be given below in a method of preparing a copper alloy in accordance with the present invention.

[Method of Preparing Copper Alloy in Accordance with the Invention]

The copper alloy in accordance with the present invention may be prepared by a method which will be described below. First, component elements according to the above-described composition are melted to cast an ingot. the acquired ingot is subjected to homogenization heat treatment at a temperature of 900-1,000° C. for 1-4 hours, and then it is immediately subjected to hot rolling at a working ratio of 85-95%. At the same time with the completion of hot rolling, the obtained product is subjected to water quenching to carry out solution treatment of solute elements, and then is subjected to cold rolling at a working ratio of 87-98%. After high strain energy is accumulated through such cold rolling and thus driving force to generate precipitates is increased, the obtained product is subjected to precipitation heat treatment at a temperature of 430-520° C. for 1-10 hours.

Subsequently, the obtained product is subjected to rolling a reduction ratio of 10-90% so that a final thickness of a finished product is determined.

In more detail, respective operations of the method of preparing the copper alloy in accordance with the present invention will be described.

First, the above-described component elements are melted to cast an ingot.

Thereafter, after the obtained product is subjected to homogenization heat treatment at a temperature of 900-1,000° C. for 1-4 hours, and then it is immediately subjected to hot rolling at a working ratio of 85-95%. Homogenization heat treatment is an essential process preparatory to hot rolling so that the ingot is hot-rolled in a sufficiently heated state rather than cold working state so as to remove a cast structure and to make a new recrystallized structure. A hot rolling is the most important operation in the method of preparing the copper alloy in accordance with the preset invention. Hot rolling conditions are factors which have an important influence on metal structures out of characteristics of an alloy, different structures after hot rolling are formed according to the hot rolling conditions and thereby characteristics of a finished product are varied. The hot rolling conditions include a hot rolling temperature, the number of times of pass in hot rolling, cooling conditions, etc., and a structure acquired after hot rolling is varied according to the respective conditions.

In order to achieve characteristics of the copper alloy in accordance with the present invention, the hot rolling temperature should be within the range of 900 to 1,000° C. When the hot rolling temperature is within such a range, an isotropic recrystallized structure having non-directionality may be acquired. As will be confirmed from Examples which will be described later, if the hot rolling temperature is lower than 900° C., a worked structure (rolled structure) remains. In a conventional copper alloy for general lead frames, in order to prevent deteriorating of characteristics of a finished product, solution treatment and a precipitation process should be added one time or more and this may cause increase in costs and lowering of productivity. On the other hand, the copper alloy in accordance with the present invention exhibits characteristics thereof without any additional process, and thus, process costs may be reduced and productivity may be improved.

When the ingot is heated to a temperature of 900-1,000° C. for 1-4 hours for homogenization heat treatment, simultaneously with acquisition of the isotropic recrystallized structure, solution treatment effects are exhibited. If the ingot is heated for a time of less than 1 hour, the worked structure locally remains and the ingot cannot completely exhibit characteristics of the isotropic recrystallized structure and, if the ingot is heated for a time exceeding 4 hours, the ingot may be partially melted. Solution treatment is a process in which an amount of elements exceeding solubility is dissolved in a Cu matrix in a supersaturated state, and thus, precipitation effects are maximized. In a general precipitation strengthening alloy, a separate additional solution treatment process is required for the alloy having a thin film thickness, and thus, process costs are increased and productivity is lowered. However, in the copper alloy in accordance with the present invention, solution treatment effects are acquired through heat treatment in the hot rolling process, and thus, high strain energy may be accumulated in the material through strong rolling at a ratio of 87-98% in a subsequent cold rolling process. High strain energy in the material serves as driving force of the precipitation process after cold rolling and thus enables uniform distribution of fine precipitates in the precipitation process.

Thereafter, at the same time with the completion of hot rolling, the obtained product from the previous step is subjected to water quenching to carry out solution treatment of the solute elements, and then it is subjected to cold rolling at a working ratio of 87-98%. High strain energy is accumulated through such cold rolling and thus driving force to generate precipitates may be increased.

Thereafter, the acquired product from the previous step is subjected to precipitation heat treatment at a temperature of 430-520° C. for 1-10 hours. The copper alloy in accordance with the present invention is a precipitation strengthening type alloy, and thus, the precipitation process is important. Further, the copper alloy in accordance with the present invention is designed so as to additionally include Mn, but since optimum strength and electrical conductivity of the copper alloy cannot be acquired by simply adding Mn, such properties are obtained by uniformly distributing fine precipitates through the precipitation process. In a conventional Cu—Fe—P-based alloy, Fe₂P precipitates are mainly present in the copper alloy but coarse FeP precipitates are locally present and thus deteriorate characteristics of the copper alloy. On the other hand, in the method of preparing the copper alloy in accordance with the present invention, precipitation heat treatment is conducted under the above conditions, and thus, fine (FeMn)₂P precipitates are distributed in the copper alloy and both high strength and high electrical conductivity may be achieved.

Finally, the obtained product from the previous step is subjected to rolling at a reduction ratio of 10-90%. Here, the product is rolled by cold rolling at a working ratio of 10-90%, thus acquiring target physical properties. Here, a preferable range of the working ratio is 30-70% and, within such a range, efficiency of a strength increment according to a working quantity of the copper alloy in accordance with the preset invention is maximized.

In addition, in the above method, after precipitation heat treatment, and prior to final rolling of the finished product, cold rolling at a working ratio of 30-90% may be executed and then intermediate heat treatment may be conducted, as needed. Such cold rolling at the working ratio of 30-90% and intermediate heat treatment are not essential and are executed so as to solve surface quality problems, such as burning (partial bonding due to heat and pressure) which may be generated due to a process or preparation conditions of precipitation heat treatment equipment of a mass production line, scratches generated due to a surface pickling process after precipitation heat treatment, etc. Intermediate heat treatment is applicable if there is a great difference between a thickness of the product after precipitation heat treatment and a thickness of the finished product after final rolling and the finished product exceeds ranges of target physical properties (strength and electrical conductivity) or it is difficult to acquire target characteristics. Here, since the main purpose of intermediate heat treatment is to reduce strength of the copper alloy but reduction in electrical conductivity of the copper alloy must be minimized, it is important to intermediate heat treat so as to reduce electrical conductivity by a range of 0.1-3% IACS. If electrical conductivity is reduced by a value of less than 0.1% IACS, heat treatment has no effect and, if electrical conductivity is reduced by a value exceeding 3% IACS, heat treatment has great effects but there is a possibility that the copper alloy deviates from target characteristics due to reduction in electrical conductivity and strength thereof.

In the method of preparing the copper alloy in accordance with the preset invention, the hot rolling and precipitation heat treatment processes have an important influence on characteristics of the finally acquired copper alloy and, in order to distribute the fine (FeMn)₂P precipitates in the copper alloy in accordance with the present invention, the hot rolling process to the precipitation process need to be sequentially controlled precisely. In order to confirm the fine precipitates generated in the copper alloy, observation using an FE-SEM and an FE-TEM is essential.

The copper alloy prepared by the method in accordance with the present invention includes the fine (FeMn)₂P precipitates and, when microstructures are observed at a magnification of 100,000× or more through crystal orientation analysis using an FE-TEM, an average particle size of the (FeMn)₂P precipitates is 50 nm or less and an area density of the (FeMn)₂P precipitates is 1.0*10¹⁰/cm² or more.

In order to observe precipitates, conventionally a TEM specimen is prepared through a general ion milling method. However, using such a specimen, it is difficult to observe fine precipitates having a particle size of several nm to tens of nm. Even if observation of fine precipitates is attempted, it is difficult to distinguish the precipitates from impurities or foreign substances in the TEM specimen prepared through the ion milling method, and crystalline structures, composition, etc. of the precipitates cannot be confirmed. On the other hand, fine precipitates in the copper alloy in accordance with the present invention may be observed through TEM analysis of a specimen, prepared through a carbon extraction replica method.

In the copper alloy in accordance with the present invention, fine (FeMn)₂P precipitates are uniformly distributed to grain boundaries and the insides of grains, and an average particle size of the (FeMn)₂P precipitates is 50 nm or less. If the average particle size of the precipitates exceeds 50 nm, electrical conductivity is inevitably lowered and poor reliability during a semiconductor process is caused. The average particle size of the precipitates may be measured through observation at a magnification of 100,000× or more through field emission transmission electron microscope (FE-TEM) crystal orientation analysis. In this regard, FIGS. 4A and 4B illustrate FE-TEM analysis results of the copper alloy in accordance with the present invention, in examples which will be descried later.

Further, an area density may be measured based on the FE-TEM results shown in FIGS. 4A and 4B. The area density is the number of precipitates present within a designated area and serves as an index to estimate distribution of precipitates. Conventionally, in order to estimate distribution of precipitates, a volume fraction is used, but the volume fraction represents a percentage of the precipitates in a designated area, and thus, if coarse particles having a great size are generated, an error range is considerable. On the other hand, if the concept of an area density is used, existence of coarse particles does not influence the area density and a degree of distribution of precipitates may be more accurately confirmed. The area density of the copper alloy in accordance with the present invention is 1.0*10¹⁰/cm² or more. Since the average particle size of the (FeMn)₂P precipitates of the copper alloy in accordance with the present invention is very fine, i.e., 50 nm or less, in order to exhibit characteristics of the copper alloy in accordance with the present invention, a large amount of the precipitates is necessary and thus if the number of the precipitates, i.e., the area density, is less than 1.0*10¹⁰/cm², the copper alloy cannot have sufficient strength.

The softening resistant temperature of the copper alloy in accordance with the present invention is 400° C. or higher. In order to exhibit sufficient softening resistant characteristics in electrical and electronic parts and semiconductors, the softening resistant temperature of the copper alloy must be 400° C. or higher. In the present invention, as a means to improve strength of the copper alloy, precipitation strengthening rather than grain refinement is executed and thus the copper alloy has excellent softening resistant characteristics. If severe plastic deformation is executed to achieve grain refinement, defective softening may occur due to high internal stress. Defective softening means lowering of hardness of a material due to heat during processing of the material and packaging of a semiconductor device, and causes a defective product.

The copper alloy for electrical and electronic parts and semiconductors in accordance with the present invention may be prepared as a sheet or a panel. Such a sheet or panel type copper alloy is suitably applied to semiconductor or IC lead frames or connectors, and terminals.

The copper alloy in accordance with the present invention has both excellent strength and electrical conductivity, as compared to conventional products, and has excellent softening resistant characteristics by mixing components for the copper alloy and precisely controlling a preparation process, as described above, and is thus suitable particularly not only for electrical and electronic parts, such as semiconductor lead frames, terminals, connectors, switches, relays, etc. which are conventionally used, but also for discrete transistors, i.e., vehicle power control semiconductors, demand for which is recently increased.

EXAMPLES Examples 1 to 16

Specimens of Examples 1 to 16 are prepared according to compositions disclosed in Table 1 below. Hereinafter, a method of preparing the specimens will be described.

Alloy elements including copper are mixed according to each of the compositions disclosed in Table 1 per 1 kg, an acquired mixture is melted in a high frequency melting furnace and then an ingot having a thickness of 20 mm, a width of 50 mm and a length of 160-180 mm is manufactured. In order to remove bad parts, such as rapid cooled parts and shrinkage cavities, bottom and top portions of the manufactured ingot are cut off by a length of 20 mm and then homogenization heat treatment of the ingot is conducted in a box furnace at a temperature of 900° C. for 2 hours. Immediately after homogenization heat treatment, hot rolling is executed at a working ratio of 90%, and solution treatment by water quenching is executed simultaneously with completion of hot rolling so as to suppress precipitation of solute elements. Prior to the precipitation process, cold rolling is executed at a working ratio of 90% such that high strain energy is accumulated through such cold rolling and thus driving force to generate precipitates is increased. Thereafter, precipitation heat treatment is executed at a temperature of 450° C. for 3 hours, and then cold rolling is executed at a working ratio of 50%. Finally, a finished product of the copper alloy is prepared as a specimen having a size of 0.3t*30w*200l and the specimen is used in a test which will be subsequently executed. Table 2 represents characteristic analysis results of prepared copper alloy specimens of Examples 1 to 16, disclosed in a Test Example.

Comparative Examples 1 to 16

Specimens of Comparative Examples 1 to 16 are prepared according to the compositions disclosed in Table 1 by the preparation method under the same conditions as Examples 1 to 16. Table 2 also represents characteristic analysis results of the prepared copper alloy specimens of Comparative Examples 1 to 16.

TABLE 1 Composition of chemical components of copper alloy Division Cu Fe P Mn Ni Sn Impurities Example 1 Remainder 0.09 0.05 0.05 — — — Example 2 Remainder 0.09 0.05 0.10 — — — Example 3 Remainder 0.09 0.05 0.15 — — — Example 4 Remainder 0.12 0.06 0.05 — — — Example 5 Remainder 0.12 0.06 0.10 — — — Example 6 Remainder 0.12 0.06 0.15 — — — Example 7 Remainder 0.12 0.06 0.12 — — — Example 8 Remainder 0.15 0.08 0.05 — — — Example 9 Remainder 0.15 0.08 0.10 — — Si 0.005 Example 10 Remainder 0.15 0.08 0.15 — — — Example 11 Remainder 0.15 0.09 0.05 — — — Example 12 Remainder 0.15 0.09 0.10 — — — Example 13 Remainder 0.15 0.09 0.15 — — — Example 14 Remainder 0.20 0.09 0.10 0.01 — — Example 15 Remainder 0.20 0.09 0.15 — 0.02 — Example 16 Remainder 0.20 0.09 0.20 0.01 0.01 — Comparative Remainder 0.12 0.04 — — — — example 1 Comparative Remainder 0.08 0.04 0.01 — — — example 2 Comparative Remainder 0.08 0.04 0.05 — — — example 3 Comparative Remainder 0.08 0.04 0.10 — — — example 4 Comparative Remainder 0.10 0.03 0.01 — — — example 5 Comparative Remainder 0.10 0.03 0.05 — — — example 6 Comparative Remainder 0.10 0.03 0.10 — — — example 7 Comparative Remainder 0.12 0.04 0.05 — — — example 8 Comparative Remainder 0.12 0.04 0.10 — — — example 9 Comparative Remainder 0.12 0.04 0.15 0.01 — — example 10 Comparative Remainder 0.12 0.04 0.20 — — — example 11 Comparative Remainder 0.15 0.04 0.10 — 0.01 — example 12 Comparative Remainder 0.15 0.04 0.20 — 0.03 — example 13 Comparative Remainder 0.15 0.10 0.10 0.03 — — example 14 Comparative Remainder 0.25 0.06 0.20 0.01 0.01 — example 15 Comparative Remainder 0.25 0.06 0.25 — — — example 16

Examples 1 to 14 are examples to evaluate critical significance of composition ranges of Cu, Fe, Mn and P, as represented in Table 1. Examples 14 to 16 are examples to confirm effects of additive elements, such as Ni and Sn. The composition of Comparative Example 1 is the same as the composition of the alloy C19210 which is widely used for lead frames. Further, the compositions of Comparative Examples 8 to 13 include Mn in addition to the composition of the alloy C19210.

[Test Example]

Hereinafter, a characteristic analysis method of the copper alloy specimens prepared according to Examples and Comparative Examples will be described.

Tensile strength is measured using a universal testing machine Z100 from ZWICK ROELL GmbH, hardness is measured by applying a load of 1kg using a Vickers hardness tester TUKON 2500 from INSTRON Co., Ltd., and electrical conductivity is measured using SIGMATEST from FOERSTER GmbH.

In softening resistant temperature analysis, heat treatment is executed using a Thermolyne 5.8L D1 Benchtop Muffle Furnace from THERMO SCIENTIFIC Co., Ltd. In more detail, after heat treatment of a specimen is executed respectively at temperatures of 300, 350, 400, 450, 500, 550, 600, 650 and 700° C. for 1 minute, hardness values of the specimen are measured, a graph of a broken line in which the Y-axis represents hardness and the X-axis represents temperature is drawn, and a temperature value intersecting a point corresponding to 80% of an initial hardness value is calculated as the softening resistant temperature. The results are shown in FIG. 1, in which the copper alloy of Example 5 is exemplarily compared to the conventional copper alloys C19400 and C19210.

An average crystal grain size of microstructures of the specimen is measured using Quanta650FEG(FE-SEM) from FEI Co., Ltd. In order to measure the average crystal grain size, after electrolyte polishing is executed on the surface of the specimen, the specimen is inserted into an FE-SEM furnace, the pressure inside the chamber is maintained to 1*10⁻⁵ torr or less and then the specimen is observed through crystal orientation analysis by irradiation with ion beams. FIG. 3 illustrates observation results of the microstructures of the copper alloy of Example 5.

In order to measure an average particle size and an area density of precipitates, JEM-2100F(FE-TEM) from JEOL Ltd. is used. In order to observe the specimen using an FE-TEM, analysis is carried out by two methods, and FIG. 4A represents results of FE-TEM analysis using a general specimen preparation method, i.e., an ion milling method. As exemplarily shown in FIG. 4A, it is difficult to confirm and analyze fine precipitates. Therefore, in order to analyze fine precipitates which cannot be confirmed using the ion milling method, FIG. 4B represents results of FE-TEM analysis of a specimen prepared by a carbon extraction replica method.

Table 2 below represents results of measurement according to the above-described characteristic analysis method.

TABLE 2 Softening Area Tensile Electrical resistant Average density of strength Hardness conductivity temp. particle size of precipitates No. (MPa) (Hv) (% IACS) (° C.) precipitates(nm) (*10¹⁰/cm²) Example 2 487 147 84 423 27 1.02 Example 3 493 148 83 419 29 1.04 Example 4 491 148 88 422 31 1.12 Example 5 521 154 87 421 30 1.24 Example 6 548 156 84 417 35 1.27 Example 7 529 153 85 425 33 1.25 Example 8 518 150 82 432 41 1.23 Example 9 527 154 85 423 38 1.28 Example 10 531 154 80 415 36 1.32 Example 11 508 149 81 426 32 1.27 Example 12 519 150 80 420 39 1.31 Example 13 529 152 78 412 41 1.41 Example 14 615 161 79 413 38 1.47 Example 15 629 164 77 410 43 1.54 Example 16 636 167 75 403 41 1.59 Comparative 445 130 89 451 56 0.012 example 1 Comparative 438 126 90 451 61 0.009 example 2 Comparative 468 132 85 444 99 0.010 example 3 Comparative 498 143 82 433 87 0.011 example 4 Comparative 427 125 90 456 72 0.008 example 5 Comparative 428 125 83 444 83 0.009 example 6 Comparative 437 131 81 425 95 0.010 example 7 Comparative 462 142 79 414 69 0.014 example 8 Comparative 476 143 77 410 103 0.016 example 9 Comparative 480 144 75 407 91 0.018 example 10 Comparative 483 145 73 403 104 0.020 example 11 Comparative 491 146 73 400 78 0.018 example 12 Comparative 503 151 69 399 112 0.022 example 13 Comparative 489 146 73 404 97 0.028 example 14 Comparative 627 169 70 391 121 1.62 example 15 Comparative 632 171 67 382 129 1.69 example 16

In Table 2 above, through comparison between Example 4 and Example 8, it may be confirmed that the copper alloy of Example 4 having a P increment in addition to the composition of the copper alloy of Example 8 provides a sufficient amount of P to form fine (FeMn)₂P precipitates and thus has both improved strength and electrical conductivity. Further, it may be confirmed from results of Example 5 that the copper alloy of Example 5 implements both excellent strength and electrical conductivity.

On the other hand, the copper alloys of Comparative Examples 1 to 16 do not satisfy strength corresponding to one of required characteristics in the industrial world, even if control of precipitates is carried out through optimization of the preparation process. The reason for this is that the copper alloys deviate from the optimum component composition of the copper alloy in accordance with the present invention and thus it is difficult to form fine (FeMn)₂P precipitates.

Out of the above-descried Comparative Examples, Comparative Examples 8 to 13 are Comparative Examples to confirm whether or not simple addition of Mn to the conventional alloy C19210 is effective. It may be confirmed from results of Comparative Examples 8 to 13 that any composition cannot satisfy the required characteristics just by simple addition of Mn. The reason for this is that simple addition of Mn cannot form (FeMn)₂P precipitates and Mn is dissolved in the Cu matrix and thus lowers electrical conductivity, and such a problem is caused by deficiency of a P content necessary to form the (FeMn)₂P precipitates. Particularly, it may be confirmed that simple solid-solution strengthening of an additive element improves strength somewhat but sharply lower electrical conductivity.

In summary of the above-described characteristic analysis results, it may be confirmed that, even if the preparation method and the analysis method, which are the same as those in Examples 1 to 16 to exhibit characteristics of the copper alloy in accordance with the present invention, are combined, the composition of the conventional copper alloy C19210 cannot exhibit improved alloy characteristics.

In order to evaluate characteristics of a copper alloy according to hot rolling temperature conditions, copper alloy specimens having the composition of Example 1 are respectively prepared under different hot rolling temperature conditions and, then, physical properties of the copper alloy specimens are evaluated.

TABLE 3 Evaluation of characteristics of copper alloy specimens having composition of Example 1 according to hot rolling conditions Tensile Electrical Softening Hot rolling strength Hardness conductivity resistant temp. (° C.) (MPa) (Hv) (% IACS) temp. (° C.) Note 870 441 131 84 432 Below both target tensile strength and hardness (in FIG. 2A) 900 472 145 87 432 Satisfying all target physical properties (in FIG. 2B) 950 476 146 87 434 Satisfying all target physical properties (in FIG. 2C)

As confirmed from Table 3, if the hot rolling temperature is lower than 900° C., characteristics of the copper alloy in accordance with the present invention are not exhibited. FIGS. 2A to 2C represent results of Table 3. FIG. 2A shows a copper alloy prepared by hot rolling at a temperature of 870° C., corresponding to general hot rolling conditions of copper alloys for lead frames and, when the copper alloy is observed after hot rolling, a worked structure (rolled structure) remains, influences the subsequent process and cause lowering of characteristics of a finished product. In copper alloys of FIGS. 2B and 2C, a hot rolling temperature is 900° C. or higher, and thus, an isotropic recrystallized structure is formed after hot rolling and characteristics of the copper alloy in accordance with the present invention may be exhibited.

In order to confirm an average crystal grain size and microstructures of the copper alloy in accordance with the present invention, an FE-SEM photograph of the copper alloy specimen prepared according to the composition of Example 5 is shown in FIG. 3. As exemplarily shown in FIG. 3, the average crystal grain size of the specimen of Example 5 is 20 μm or less and a standard deviation thereof is 5 μm or less. From such results, it may be confirmed that the copper alloy in accordance with the present invention has good microstructures and may thus be used in electrical and electronic parts and semiconductors without any problems, such as surface defects.

Analysis results of the copper alloy specimen of Example 5 using the FE-TEM are shown in FIGS. 4A and 4B.

FIG. 4A is an FE-TEM photograph of a specimen prepared by the ion milling method which is generally used, so as to confirm precipitates in the copper alloy having the composition of Example 5 and, in this FE-TEM photograph, it is difficult to confirm existence of precipitates in the copper alloy and whether or not the precipitates are distributed in the copper alloy and thus accurate analysis is difficult. In order to solve such problems, a new analysis method must be employed.

In order to overcome limits of the conventional ion milling method, FIG. 4B is an FE-TEM photograph of a specimen prepared by the carbon extraction replica method so as to confirm precipitates in the copper alloy having the composition of Example 5. If the specimen prepared by the carbon extraction replica method is observed, analysis including shapes, sizes, composition, area density, etc. of the fine precipitates may be accurately carried out. It may be confirmed from FIG. 4A that precipitates exist only, but it may be confirmed from FIG. 4B that (FeMn)₂P precipitates, which are not observed in the conventional Cu—Fe—P-based alloys, are uniformly formed and have an average particle size of 50 nm or less and an area density of 1.01*10¹⁰/cm² or more. 

1: A copper alloy for electrical and electronic parts and semiconductors, comprising: 0.09 to 0.20% by mass of iron (Fe) 0.05 to 0.09% by mass of p hosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of copper (Cu) and 0.05% by mass or less of inevitable impurities, the inevitable impurities comprising at least one selected from the group consisting of Si, Zn, Ca, Al, Ti, Be, Cr, Co, Ag and Zr; and (FeMn)₂P precipitates, wherein: the (FeMn)₂P precipitates are measured by observing a specimen prepared by a carbon extraction replica method using a high-resolution transmission electron microscope (HR-TEM) or a field emission transmission electron microscope (FE-TEM) at a magnification of 100,000× or more, and have an average particle size of 50 nm or less and an area density of 1.0*10¹⁰/cm² or more; and the copper alloy has tensile strength of 470 MP or ore, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or higher. 2: The copper alloy for electrical and electronic parts and semiconductors according to claim 1, wherein the impurities have a content of 0.01% by mass or less. 3: The copper alloy for electrical and electronic parts and semiconductors according to claim 1, further comprising 0.0001 to 0.03 % by mass of at least one of Ni or Sn. 4: The copper alloy for electrical and electronic parts and semiconductors according to claim 1, wherein the copper alloy has an average crystal grain size of 20 μm or less and a standard deviation of 5 μm or less, out of crystal grain sizes measured by crystal orientation analysis using a field emission scanning electron microscope (FE-SEM). 5: The copper alloy for electrical and electronic parts and semiconductors according to claim 1, wherein the copper alloy is prepared as a sheet or a panel. 6: A method of preparing a copper alloy for electrical and electronic parts and semiconductors, comprising: melting the component elements of the copper alloy to cast an ingot, wherein the component elements comprise: 0.09 to 0.20% by mass of iron (Fe), 0.05 to 0.09% by mass of phosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of cooper (Cu) and 0.05% by mass or less of inevitable impurities, the inevitable impurities comprising at least one selected from the group consisting of Si, Zn, Ca, Al, Ti. Be, Cr, Co, Ag and Zr; and (FeMn)₂P precipitates, wherein: the (FeMn)₂P precipitates are measured b observing a specimen prepared by a carbon extraction replica method using a high-resolution transmission electron microscope (HR-TEM) or a field emission transmission electron microscope (FE-TEM) at a magnification of 100,000× or more, and have an average particle size of 50 nm or less and an area density of 1.0*10¹⁰/cm² or more; and the copper alloy has tensile strength of 470 MPa or more, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or higher; homogenization heat treating the acquired ingot at a temperature of 900-1,000° C. for 1-4 hours, and then hot rolling at a working ratio of 85-95%; cold rolling the obtained product from the previous step at working ratio of 87-98%; precipitation heat treating the obtained product from he previous step at a temperature of 430-520° C. for 1-10 hours; and rolling the obtained product from the previous step at a reduction ratio of 10-90% to produce a finished product. 7: The method according to claim 6, wherein impurities have a content of 0.01 by mass or less.. 8: The method according to claim 6, wherein the copper alloy comprises 0.0001 to 0.03% by mass of at least one of Ni or Sn. 9: The method according to claim 6, wherein the copper alloy has an average crystal grain size of 20 μm or less and a standard deviation of 5 μm or less, out of crystal grain sizes measured by crystal orientation analysis using a field emission scanning electron microscope (FE-SEM). 10: The method according to claim 6, wherein the copper alloy is prepared as a sheet or a panel. 11: A method of preparing a copper alloy for electrical and electronic parts and semiconductors, comprising: melting component elements of the copper alloy to cast an ingot, wherein the component elements comprise: 0.09 to 0.20% by mass of iron (Fe), 0.05 to 0.09% by mass of phosphorous (P), 0.05 to 0.20% by mass of manganese (Mn), the remaining amount of copper (Cu) and 0.05% by mass or less of inevitable impurities, the inevitable impurities comprising at least one selected from the group consisting of Si, Zn, Ca, Al, Ti Be, Cr, Co, Ag and Zr, wherein the impurities have a content of 0.01% by mass or less; and (FeMn)₂P precipitates, wherein: the (FeMn)₂P precipitates are measured by observing a specimen prepared by a carbon extraction replica method using a high-resolution transmission electron microscope (HR-TEM) or a field emission transmission electron microscope (FE-TEM) at a magnification of 100,000× or more, and have an average particle size of 50 nm or less and an area density of 1.0*10¹⁰/cm² or more; end the copper alloy has tensile strength of 470 MPa or more, hardness of 145 Hv or more, electrical conductivity of 75% IACS or more and a softening resistant temperature of 400° C. or higher; homogenization heat treating the acquired ingot at a temperature of 900-1,000° C. for 1-4 hours, and then hot rolling at a working ratio of 85-95%; cold rolling the obtained product from the previous step at a working ratio of 87-98%; precipitation heat treating the obtained product from the previous step at a temperature of 430-520° C. for 1-10 hours; and rolling the obtained product from the, previous step at a reduction, ratio of 10-90% to produce a finished product. 12: The method according to claim 11, wherein the copper alloy comprises 0.0001 to 0.03% by mass of at least one of Ni or Sn. 13: The method according to claim 11, wherein the copper alloy has an average crystal grain size of 20 μm or less and a standard deviation of 5 μm or less, out of crystal grain sizes measured by crystal orientation analysis using a field emission scanning electron microscope (FE-SEM). 14: The method according to claim 11, wherein the copper alloy is prepared as sheet or a panel. 